The invention pertains generally to magnetostrictive devices and in particular to components to magnetostrictive devices prepared from iron-boron-rare earth alloys.
Electrical signals can be converted into mechanical displacements, or the reverse, using the magnetostrictive effect by placing a magnetostrictive material in the magnetic field of a solenoid. A changing current in the solenoid changes the magnetic state of the magnetostrictive material, thereby changing its physical dimensions. Conversely, a change in the physical dimension induces a voltage and/or current in the solenoid. Very important properties of a magnetostrictive material are the size of the magnetostrictive effect and how much applied magnetic field is required to achieve it. In general a good magnetostrictive material has high electrical resistivity, low magnetic anisotropy, large magnetization, and large isotropic magnetostriction. All crystalline materials have some magnetic anisotropy as well as magnetostriction which is not perfectly isotropic.
The largest room temperature magnetostrictive strains are exhibited by rare earth-iron Laves phase (RFe.sub.2) intermetallic compounds, disclosed in Koon et al. Phys. Lett. 37A:5, p. 413 (1971). In Crystalline Electric Field and Structural Effects in f-Electron Systems J. E. Crow et al. eds. Plenum, N.Y. 1981, pp. 75-82, it is taught that the magnetic anisotropy of such compounds can be made small by employing special combinations of elements, such as Ho.sub..58 Tb.sub..20 Dy.sub..22 Fe.sub.2. However, this and other similar alloys also have the problem that their magnetostrictive is very anisotropic, with large strains occuring along the (111) direction and very small ones along (100). To produce a large magnetostrictive effect in such an alloy with very low applied magnetic fields requires using either a single crystal or a highly textured polycrystalline sample. Generally alloys which do not contain rare earth elements have much smaller magnetostrictive strains than those exhibited by the rare earth-iron Laves phase (RFe).sub.2 compounds. Disadvantages of the RFe.sub.2 compounds are they must contain 331/3 at. % rare earth, which is expensive; they must employ special combinations of rare earths to reduce magnetic anisotropy; and generally they must employ very high purity materials, which adds to the expense. They also need to be textured, which adds extra processing expense.
Since amorphous magnetic alloys are inherently isotropic, these alloys would avoid these problems. Unfortunately amorphous magnetic alloys are difficult to produce and they generally have poor magnetostriction. Amorphous magnetic alloys between strongly magnetic transition metals and the rare earth elements can be prepared by several methods. Among the easiest are coevaporation or sputtering onto cold substrates. Such methods, however, produce very small amounts of material with very high bulk costs, and are not practical for most applications. For use in applications where bulk quantities are required, some method involving rapid quenching from the melt is necessary. Because of the much slower quench rate from a liquid compared to that from sputtering or evaporation, most amorphous melt quenched alloys are at compositions near deep eutectics in the phase diagrams. For rate earth-transition metal alloys the deep eutectic points occur near R.sub..65 TM.sub..35, so that such amorphous alloys contain large amounts of rare earth and smaller amounts of the transition metals. This is unsatisfactory for at least two reasons. The first is that the strength of the exchange interactions depend on the amount of transition metal, so that all such alloys have relatively low magnetic transition temperatures and are thus not very useful at room temperature. Second is that the rare earth component of the alloy is expensive, so that an alloy containing mostly rare earth is very costly. To preserve the strength of the magnetic interactions it is generally necessary to have an alloy containing mostly transition metals, and thus having a binary composition very far from the eutectic (and thus very difficult to make). Thus, until now, it was necessary to chose between excellent but expensive magnetostrictive devices and moderately good and moderately expensive magnetostrictive devices.